A prior apparatus in this field is disclosed, for instance, in FIG. 1 of Japanese Patent-Laid Open No. 62-120829 (1987) published on June 2, 1987 entitled "Charging apparatus for a small size vacuum cleaner", which equips a transformer for transforming a power-frequency voltage to a voltage which is necessary for charging a battery, the primary winding of the transformer is connected to the power-frequency voltage, and the secondary winding of the transformer is connected to the battery through a connecting terminal.
When the apparatus enclosing the battery of the prior art mentioned above finishes the charging of the battery or is not necessary to charge the battery, a reverse current from the battery to the charging circuit flows through the connecting terminal. For preventing such a leakage of the current to the battery, it is necessary to provide a relay contact which opens its contact for interrupting power supply from the electric power source to the battery when the charging of the battery does not take place. Accordingly, for attaining the above-mentioned demand, it is necessary to add a connecting portion of a signal wire for closing and opening the relay contact to the connector terminal. When a battery terminal connected to the connector terminal is made wet by water, the battery current flows in reverse so that unnecessary discharge and power consumption of the battery are caused and performance of the battery is not maintained.